Bridge failure a possible cause in Houston County train derailment

From AP Bridge failure a possible cause in Houston County train derailment
Brownsville, Minn. (AP) — A train derailment in southeastern Minnesota near Reno could be related to the failure of a wooden railroad bridge.
Department of Public Safety spokesman Doug Neville says it’s not clear if the privately owned bridge collapsed under the train, or if derailed cars took it out.
The derailed train is owned by the Iowa, Chicago & Eastern Railroad, but it’s also unclear if that railroad also owns the bridge.

A Theory of Modes

Wikipedia’s article List of transport topics gives a list of a variety of modes largely defined by their technology (are they powered by animals or engines, are the engines on the vehicle or is the vehicle powered by a cable, do the vehicles travel on land, sea, or water, etc. While this is a reasonably comprehensive list and a reasonable organization of the subject for wikipedia, it does not really get at the transportation aspect of modes, focusing instead on their mechanical aspects.
I propose a schema that classifies passenger modes according to how they operate, not how they are paid for or what technology is employed:
The key attributes are:
* Availability (can you travel on demand, is a vehicle easily hailed, or is a reservation required?),
* Accompaniment (can your party travel alone, or is the ride shared with others?),
* Fixity of route ends (are the origin and destination of the route fixed?),
* Fixity of route stops (are the stops fixed, or does the vehicle stop anywhere between the origin and destination?),
* Fixity of schedule (does the vehicle adhere to a schedule?),
* Driver (does the party drive itself or rely on others?).
In this way, we can see the similarity or differences of seemingly different or similar modes.

Accompaniment Route Ends Driver Stops Schedule Example
On-demand          
Own Party Variable Self Variable Variable Car
          Motorcycle
          Bicycle
          Walking
          Carpool
           
  Variable Other Variable Variable Taxi
  Fixed Other Variable Variable PRT
           
Shared Variable Other Variable Variable Shared Taxi
  One end fixed Other Variable Variable Airport Express, Hotel Van
           
  Two ends fixed Other Variable Variable Jitney
    Other   Fixed Schedule Bus
    Other Fixed Stops Variable Elevator, People Mover
    Other   Fixed Schedule Rail, BRT
    Other Nonstop Variable Stagecoach
          Express Bus/Train
By reservation         Airline
Own Party Variable ends Self     Limosine
    Other     Car Share, Car Rental
Shared Variable ends       Paratransit